An inflatable vehicle occupant protection device, such as an air bag, is part of an apparatus which further includes a crash sensor and an inflator. When the crash sensor senses a vehicle crash having at least a predetermined threshold level of severity, the inflator is actuated. The inflator then emits inflation fluid which inflates the air bag into the vehicle occupant compartment to help protect an occupant of the vehicle.
The source of inflation fluid may comprise a body of material which, when ignited, rapidly generates a large volume of inflation gas. Typically, such a body of gas generating material is contained in a cylindrical combustion chamber in the inflator and has a corresponding cylindrical configuration. The body of gas generating material may be defined by a single cylindrical piece of gas generating material or by a stack or row of short cylindrical pieces which are known as grains. The body of gas generating material may alternatively be defined by tablets of gas generating material which fill the combustion chamber. In each case, the combustion chamber is sealed hermetically to protect the body of gas generating material from the ambient atmosphere.